83 research outputs found
Comparison of Passive and Semi-Active Horizontal Platform Suspensions
In this paper modelling, control and optimization of a kinematically excited horizontal platform is presented. The platform with two independent mutually perpendicular suspension units is designed to mitigate horizontal vibration of the operator seat in the excavator cabin. Three types of suspension between the lower part of the platform and the cabin and between the lower part and the upper part of the platform are investigated, namely passive suspension, idealized semi-active suspension and suspension equipped with magnetorheological dampers. Their design parameters are optimized. The improvement of the magnetorheological/idealized semi-active platform suspension in reducing the vibration total value of the frequency weighted effective accelerations in two mutually perpendicular horizontal directions, compared with the passive platform suspension, is 26,3%/70,8%. The magnitude of the vibration total value of the passive/magnetorheological/idealized semi-active platform suspension is 0,4547m·sâ2 (a little uncomfortable)/0,3352 m·sâ2 (a little uncomfortable)/0,1328 m·sâ2 (not uncomfortable)
Understanding Calculus Through Maple-Based Dynamic Visualization Tools
First-year college students experience difficulties in understanding the concepts of derivatives and integrals. At the postsecondary level, the use of static visualization and other traditional instruction delivery methods often are unable to meet students\u27 needs in calculus. This problem is current and essential in the field of education and needs consideration to enhance the method of teaching calculus. The rationale for this study was to scrutinize the effects of Maple dynamic visualization instructional activities, within the framework of the animation-visualization theory, on students\u27 conceptual and procedural understanding of differential and integral calculus. The usage of a quantitative 2x2 factorial pretest-posttest control group quasi-experimental mixed design, with multivariate analysis of variance for data (de-identified list of 81 students\u27 test scores on derivatives and integrals) analyses, helped examine the relationships between the research variables. Results showed that the Maple dynamic visualization group, significantly (p \u3c 0.001), outperformed the non-Maple static visualization group with a significant interaction between the groups with a substantial effect size of at least 0.27. This study augments the body of evidence that supported the efficacy of animated visuals over static visuals in producing more exceptional academic performance. A future researcher should use the random assignment to groups to minimize the possibilities of nonequivalent groups and the same measure for pretest and posttest. This study provides a groundwork for positive social change to reach a shared vision in education, enable learners to gain skills in calculus, and prepare students in and for science, technology, engineering, and mathematics majors and careers
Analysis the brachistochronic motion of a mechanical system with nonlinear nonholonomic constraint
U ovom radu analizira se problem brahistohronog ravnog kretanja mehaniÄkog sistema sa nelinearnom neholonomnom vezom. Neholonomni mehaniÄki sistem je predstavljen sa dva Äapljiginova seÄiva, zanemarljivih dimenzija, koja nameÄu nelinearno ograniÄenje u vidu upravnosti brzina. Razmatra se brahisthrono ravno kretanje pri zadatom poÄetnom i krajnjem poloĆŸaju uz neizmenjenu vrednost mehaniÄke energije u toku kretanja. Diferencijalne jednaÄine kretanja, u kojima figuriĆĄu reakcije neholonomnih veza i upravljaÄkih sila, dobijene su na osnovu opĆĄtih teorema dinamike. Ovde je to podesnije umesto nekih drugih metoda analitiÄke mehanike primenjenih na neholonomne mehaniÄke sisteme u kojima je neophodno dati naknadno fiziÄko tumaÄenje mnoĆŸitelja veza. Formulisan brahistohroni problem, uz odgovarajuÄi izbor veliÄina stanja je reĆĄen kao, najjednostavniji u ovom sluÄaju, zadatak optimalnog upravljanja primenom Pontryagin-ovog principa maksimuma. Dobijen je odgovarajuÄi dvotaÄkasti graniÄni problem sistema obiÄnih nelinearnih diferencijalnih jednaÄina koji je neophodno numeriÄki reĆĄiti. NumeriÄki postupak za reĆĄavanje dvotaÄkastog graniÄnog problema vrĆĄi se metodom ĆĄutinga. Na osnovu tako dobijenog brahistohronog kretanja odreÄuju se aktivne upravljaÄke sile, a ujedno i reakcije neholonomnih veza. KoristeÄi Kulonove zakone trenja klizanja, odreÄuje se minimalno potrebna vrednost koeficijenta trenja klizanja, tako da se razmatrani sistem kreÄe u skladu sa neholonomnim zadrĆŸavajuÄim vezama.This paper analyzes the problem of brachistochronic planar motion of a mechanical system with nonlinear nonholonomic constraint. The nonholonomic system is represented by two Chaplygin blades of negligible dimensions, which impose nonlinear constraint in the form of perpendicularity of velocities. The brachistrochronic planar motion is considered, with specified initial and terminal positions, at unchanged value of mechanical energy during motion. Differential equations of motion, where the reactions of nonholonomic constraints and control forces figure, are obtained on the basis of general theorems of mechanics. Here, this is more convenient to use than some other methods of analytical mechanics applied to nonholonomic mechanical systems, where a subsequent physical interpretation of the multipliers of constraints is required. The formulated brachistochrone problem, with adequately chosen quantities of state, is solved as simple a task of optimal control as possible in this case by applying the Pontryagin maximum principle. The corresponding two-point boundary value problem of the system of ordinary nonlinear differential equations is obtained, which has to be numerically solved. Numerical procedure for solving the two-point boundary value problem is performed by the method of shooting. On the basis of thus obtained brachistochronic motion, the active control forces, along with the reactions of nonholonomic constraints, are defined. Using the Coulomb friction laws, a minimum required value of the coefficient of sliding friction is defined, so that the considered system is moving in accordance with nonholonomic bilateral constraints
Elements of dynamic parameters modification and sensitivity
Promene na konstrukcijama mogu izazvati promene u strukturnim matricama nekih elemenata. U zavisnosti od vrste konstrukcije, kao i od ĆŸeljenih promena u njoj, moguÄe je menjati veÄu ili manju grupu elemenata. U ovom radu se analiziraju efekti malih i velikih modifikacija grupa elemenata na sopstvene vrednosti i frekvencije. Analiza se vrĆĄi koriĆĄÄenjem kompjuterskih programa zasnovanim na metodi konaÄnih elemenata i implementaciji distribucije potencijalne i kinetiÄke energije na glavnim oblicima oscilovanja u posmatranim elementima konstrukcije.Structural modifications can cause changes in the matrices of some elements. Depending on the type of structure, or a desired change, a group of elements can be modified. This paper analyzes the effects of small and large-scale modifications of some groups of elements on structural eigenvalues and frequencies. The process of analysis is done using a computer program, based on using of finite element methods and the implementation of structure energy distributions
Analysis the brachistochronic motion of a mechanical system with nonlinear nonholonomic constraint
U ovom radu analizira se problem brahistohronog ravnog kretanja mehaniÄkog sistema sa nelinearnom neholonomnom vezom. Neholonomni mehaniÄki sistem je predstavljen sa dva Äapljiginova seÄiva, zanemarljivih dimenzija, koja nameÄu nelinearno ograniÄenje u vidu upravnosti brzina. Razmatra se brahisthrono ravno kretanje pri zadatom poÄetnom i krajnjem poloĆŸaju uz neizmenjenu vrednost mehaniÄke energije u toku kretanja. Diferencijalne jednaÄine kretanja, u kojima figuriĆĄu reakcije neholonomnih veza i upravljaÄkih sila, dobijene su na osnovu opĆĄtih teorema dinamike. Ovde je to podesnije umesto nekih drugih metoda analitiÄke mehanike primenjenih na neholonomne mehaniÄke sisteme u kojima je neophodno dati naknadno fiziÄko tumaÄenje mnoĆŸitelja veza. Formulisan brahistohroni problem, uz odgovarajuÄi izbor veliÄina stanja je reĆĄen kao, najjednostavniji u ovom sluÄaju, zadatak optimalnog upravljanja primenom Pontryagin-ovog principa maksimuma. Dobijen je odgovarajuÄi dvotaÄkasti graniÄni problem sistema obiÄnih nelinearnih diferencijalnih jednaÄina koji je neophodno numeriÄki reĆĄiti. NumeriÄki postupak za reĆĄavanje dvotaÄkastog graniÄnog problema vrĆĄi se metodom ĆĄutinga. Na osnovu tako dobijenog brahistohronog kretanja odreÄuju se aktivne upravljaÄke sile, a ujedno i reakcije neholonomnih veza. KoristeÄi Kulonove zakone trenja klizanja, odreÄuje se minimalno potrebna vrednost koeficijenta trenja klizanja, tako da se razmatrani sistem kreÄe u skladu sa neholonomnim zadrĆŸavajuÄim vezama.This paper analyzes the problem of brachistochronic planar motion of a mechanical system with nonlinear nonholonomic constraint. The nonholonomic system is represented by two Chaplygin blades of negligible dimensions, which impose nonlinear constraint in the form of perpendicularity of velocities. The brachistrochronic planar motion is considered, with specified initial and terminal positions, at unchanged value of mechanical energy during motion. Differential equations of motion, where the reactions of nonholonomic constraints and control forces figure, are obtained on the basis of general theorems of mechanics. Here, this is more convenient to use than some other methods of analytical mechanics applied to nonholonomic mechanical systems, where a subsequent physical interpretation of the multipliers of constraints is required. The formulated brachistochrone problem, with adequately chosen quantities of state, is solved as simple a task of optimal control as possible in this case by applying the Pontryagin maximum principle. The corresponding two-point boundary value problem of the system of ordinary nonlinear differential equations is obtained, which has to be numerically solved. Numerical procedure for solving the two-point boundary value problem is performed by the method of shooting. On the basis of thus obtained brachistochronic motion, the active control forces, along with the reactions of nonholonomic constraints, are defined. Using the Coulomb friction laws, a minimum required value of the coefficient of sliding friction is defined, so that the considered system is moving in accordance with nonholonomic bilateral constraints
Variation de la densitĂ© et la couleur du bois de Pterocarpus erinaceus (Poir) en fonction des conditions environnementales en Afrique de lâOuest
National audiencePterocarpus erinaceus (Poir.) is currently spontaneous species of Guinea-Sudanese and Sudano-Sahelian areas overexploited and threatened in West Africa. This paper analyzes the density and color of the wood of the species in the agro-ecological zones of three countries in West Africa (Togo, Burkina Faso and Niger). The results of 452 samples collected from 95 trees from the three countries show significant differences in values of basic density and color parameters (P <0.05) according to agro-ecological zones (Sudan, Guinea and Sahel). At scale intra-tree, even if there is an increase in density with the number of rings counted from the pith, this increase is very small (RÂȆ0.18). This reflects the fact that age has little influence on the trees density. In addition, a significant correlation was observed between density and color parameters.Pterocarpus erinaceus (Poir.) est actuellement lâespĂšce spontanĂ©e des zones guinĂ©o-soudaniennes et soudano-sahĂ©liennes trĂšs exploitĂ©e et menacĂ©e en Afrique de lâOuest. Le prĂ©sent travail analyse la densitĂ© et la couleur du bois de lâespĂšce dans les zones agroĂ©cologiques de trois pays de lâAfrique de lâOuest (Togo, Burkina Faso et Niger). Les rĂ©sultats obtenus sur 452 Ă©prouvettes prĂ©levĂ©es de 95 arbres issus des 3 pays indiquent des diffĂ©rences significatives des valeurs de lâinfradensitĂ© et des paramĂštres de couleur (P<0,05) en fonction des zones agro-Ă©cologiques (soudanienne, guinĂ©enne et sahĂ©lienne). A lâĂ©chelle intra-arbre, mĂȘme sâil ya une augmentation de la densitĂ© en fonction du nombre de cernes comptĂ©s, depuis la moelle, cette augmentation est trĂšs faible (RÂȆ0,18). Ce qui traduit le fait que lâĂąge des arbres influence peu lâinfradensitĂ©. Par ailleurs une corrĂ©lation significative a Ă©tĂ© observĂ©e entre la densitĂ© et les paramĂštres de couleur
A Google-inspired error-correcting graph matching algorithm
Graphs and graph algorithms are applied in many different areas including
civil engineering, telecommunications, bio-informatics and software engineering.
While exact graph matching is grounded on a consolidated theory and
has well known results, approximate graph matching is still an open research
subject.
This paper presents an error tolerant approximated graph matching algorithm
based on tabu search using the Google-like PageRank algorithm. We report preliminary
results obtained on 2 graph data benchmarks. The first one is the TC-15
database [14], a graph data base at the University of Naples, Italy. These graphs
are limited to exact matching. The second one is a novel data set of large graphs
generated by randomly mutating TC-15 graphs in order to evaluate the performance
of our algorithm. Such a mutation approach allows us to gain insight not
only about time but also about matching accuracy
Ăvaluation de la productivitĂ© technique de trois matĂ©riels dâĂ©tuvage de riz paddy au BĂ©nin
Objectif : Lâobjectif du travail est dâĂ©valuer la productivitĂ© technique de trois Ă©quipements dâĂ©tuvage de riz paddy, notamment :-i- le petit kit (marmite+bac) dâune capacitĂ© dâĂ©tuvage de 80 kg par traitement, -ii- le tonneau basculant dâune capacitĂ© de 80 kg et -iii- le grand kit dâune capacitĂ© de 300 kg.MĂ©thodologie et rĂ©sultats : La productivitĂ© technique de chacun de ces trois Ă©quipements en usage au BĂ©nin a Ă©tĂ© Ă©valuĂ©e par rapport Ă : la main dâoeuvre/travail (kg de paddy traitĂ© /Homme/heure), lâutilisation de bois (kg de paddy traitĂ©/kg de bois), lâeau (kg paddy traitĂ©/Litre dâeau) et lâinvestissement (kg de paddy étuvĂ© /100 FCFA investis). Par la suite, les attributs de qualitĂ© physique du riz tels que le coeur blanc, lâhomogĂ©nĂ©itĂ©, la duretĂ© et la couleur ont Ă©tĂ© Ă©valuĂ©s sur les Ă©chantillons du riz Ă©tuvĂ© avec chaque matĂ©riel dâĂ©tuvage. Les rĂ©sultats obtenus indiquent que le grand kit de 300 kg prĂ©sente une productivitĂ© de travail plus faible (8,98 kg) que les deux autres matĂ©riels dâĂ©tuvage. Le kit bac+marmite et le matĂ©riel d'Ă©tuvage tonneau prĂ©sentent des productivitĂ©s similaires par rapport Ă la main-d'oeuvre, lâutilisation de bois, lâeau et le capital investi. Aucune diffĂ©rence significative nâest observĂ©e pour la consommation en eau pour les trois matĂ©riels testĂ©s. A lâexception de la couleur, la qualitĂ© physique du riz Ă©tuvĂ© avec les trois matĂ©riels ne montre aucune diffĂ©rence significative pour le coeur blanc, lâhomogĂ©nĂ©itĂ© et la duretĂ© des grains de riz.Conclusion et application des rĂ©sultats : Vu la qualitĂ© de riz Ă©tuvĂ© obtenu aprĂšs utilisation de ces matĂ©riels, le kit bac+marmite ou le kit de grande capacitĂ© de 300 kg peuvent ĂȘtre recommandĂ©s aux femmes étuveuses en fonction de leur niveau de production. Toutefois des travaux dâamĂ©liorations sont nĂ©cessaires aussi bien sur le grand kit de 300kg que sur celui en tonneau afin de faciliter leur utilisation et de permettre aux transformatrices de produire de riz Ă©tuvĂ© de bonne qualitĂ©.Mots-clĂ©s : productivitĂ©, matĂ©riel, Ă©tuvage de riz, qualitĂ©.Assessment of the productivity of three parboiling equipments in BeninABSTRACTObjective: To evaluate the productivity of three parboiling equipments namely: small kit (Pot + vat with parboiling capacity of 80 kg); barrel of with a capacity of 80 kg and the big kit (tank + vat with a capacity of 300 kg).Methodology and results: The productivity of these three equipments was evaluated with respect to: labor (kg of paddy processed/person/ hour), fire wood (kg paddy processed/kg), water (kg paddy/kg/liter), investment (kg paddy/100FCFA). Thereafter, the physical quality attributes of the parboiled rice such as chalkiness, homogeneity, toughness and the colour of the parboiled rice samples were evaluated. The results indicate that the 300 kg big kit presented low labor productivity of 8.98kg compared to the two other parboiling materials. The small kit (Pot + vat of parboiling capacity 80 kg) and the barrel of a capacity 80 kg present similar productivity in relation to the labor, wood, water and investment. No significant difference is observed for water use during parboiling while using each of the tested materials. Except for the colour, the physical quality of parboiled rice obtained with each of the three materials shows no significant difference for the chalkiness, homogeneity and the toughness of the rice grains.Conclusion and application of results: Concerning the quality of parboiled rice obtained after use of these materials, the small kit or the big kit (tank + vat with a 300 kg capacity) can be recommended to the women parboilers according to their level of production. However, works of improvement are necessary on the big kit of 300kg as well as that of barrel in order to facilitate their use and to allow the processors to produce good quality parboiled rice.Key words: Productivity, equipment, rice, parboiling, quality
EspÚces Ligneuses de Savanes SÚches du Nord du Togo : Considérations Socioculturelles et Relations de Pouvoir des Parties Prenantes
Les espĂšces ligneuses du nord du Togo sont sujettes Ă de diverses utilisations pour satisfaire des besoins multiples des populations et leur gestion implique plusieurs acteurs. Lâobjectif de lâĂ©tude est dâapprĂ©cier les connaissances endogĂšnes de ces espĂšces ligneuses, les prĂ©fĂ©rences et les similaritĂ©s. Lâapproche mĂ©thodologique est basĂ©e sur des enquĂȘtes ethnobotaniques et socioĂ©conomiques menĂ©es auprĂšs de 14 groupes ethniques par interview individuel et par focus groups. Les analyses ont portĂ© sur la Classification Ascendante HiĂ©rarchique (CAH) des usages selon la mĂ©thode de Sorensen et sur la catĂ©gorisation des parties prenantes. Au sein des diffĂ©rents groupes socioculturels ciblĂ©s, il ressort un consensus, notamment sur les espĂšces utilisĂ©es pour une catĂ©gorie dâusage donnĂ©e. Lâutilisation courante des espĂšces ligneuses est orientĂ©e simultanĂ©ment sur deux grands types dâusages Ă savoir : (i) usages alimentaires, mĂ©dicinaux, fourragĂšres et rituels ; et (ii) usages artisanal, bois Ă©nergie et bois de service. Elle est rare pour un type spĂ©cifique dâusages cosmĂ©tiques ou hygiĂ©niques. Ces usages sont similaires Ă quatre grands regroupements ethniques. Le rĂ©sultat des inventaires rĂ©alisĂ© sur lâensemble des espĂšces ligneuses montrent que, 42 de ces espĂšces prĂ©sentent une vulnĂ©rabilitĂ© forte. Les rĂ©alitĂ©s socioculturelles et la promiscuitĂ© entre les groupes ethniques dĂ©terminent les connaissances et les choix de biens et services Ă©cosystĂ©miques. Ainsi, il est recommandĂ© que les programmes dâamĂ©nagements forestiers tiennent compte de ces facteurs y compris, les responsabilitĂ©s locales de mĂȘme que les influences et les intĂ©rĂȘts des parties prenantes.
Woody species in northern Togo are used to meet multiple needs of populations and their management involves many actors. The study objective is to appreciate communitiesâ knowledge of these woody species, preferences, and similarities. The methodology is based on semi-directive ethnobotanical and socioeconomic surveys within 14 ethnic groups through individual interviews and focus groups discussions. The analysis included Hierarchical Upward Classification (HUC) of uses according to the Sorensen method, and on the characterization of the main stakeholders. Within the targeted various socio-cultural groups, there is a consensus, mainly on the species used for a given category of use. It emerges that woody species are frequently used for two goals (food and medicinal; livestock feeding and ritual), or three goals (artisanal, energy wood, and service wood) and rarely for a specific type of use (cosmetic or hygienic). Four main ethnic groups have similarities of uses and 42 out of all of the species identified, present a high vulnerability. Some local socio-cultural realities and promiscuity between ethnic groups determine the knowledge of forest trees and the choices of goods and services. Therefore, it is recommended for forest development programs to take into account the above factors including local responsibilities as well as influences and interests of stakeholders
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